Magnetic tape media have been used for many years as a data storage or record medium, particularly for data interchange. Such magnetic tape media started out with a few (7-9) record or data tracks. Even with such few tracks, magnetic tape media and the associated tape drives exhibited several error causing characteristics. Error detection and correction systems have been widely employed to accommodate and correct errors arising in the storage and retrieval of data on and from such magnetic tape media. Over the years, it has also been desired that the areal recording density be increased. In achieving this desire, error detection and correction systems have been successfully used. Such error detection and correction systems had many restraints, that is, the error detection and correction should either provide error detection and correction in "real time" or with a minimal delay in error detection and correction data processing.
Currently, it is desired that one-half inch magnetic tape media employ a number of tracks in the hundreds, such as 128, etc. Concurrently, the longitudinal density has also been substantially increased to more than 2500 flux changes per millimeter. Such higher longitudinal and track densities create greater sensitivities that result in greater number of data errors. Media surface perturbations, head to medium relationships and the like co-act to create error-prone recording and reproduction. It is known that such error-prone conditions can be alleviated by dispersing the recording of data from each data record, block, file, etc. over a magnetic tape medium. It is also desired to provide for such dispersal in a minimal area for facilitating rapid recording and reproduction of data. According to the present invention, such dispersal can be in a minimal area yet provide enhanced recording and reproduction reliability by dispersing the data in accordance with the error detecting and correcting data format. Such dispersal is provided such that advantages of the dispersal are achieved with a variety of track densities without changing the basic data format. Therefore, the data format plays an important role in obtaining high quality data recording and reproduction.
An error producing magnetic tape media syndrome is a change in signal-to-noise ratios (SNR). The lower the SNR, the greater the probability of causing a data error. Accordingly, it is desired to employ error detection and correction (ECC) systems in a manner for accommodating reduced SNR.
A known error detection and correction algorithm is the so-called BCH codes. A simplified subset of the BCH codes are the well known Reed-Solomon codes. Many types of error detection and correction coding have been used with recording and reproduction on and from magnetic tape media. So-called error pointers have been used to enhance the error correction capabilities of all ECC systems. So-called "dead tracking" has been used in magnetic tape media to indicate that a read circuit for the so-called "dead track" is so out of synchronism with the read signal that no valid data are being sensed from the one track--this fact is a pointer for the ECC that all signals from the dead track are in error. Other error pointers have been used over the years for error pointing. Of course, some of the error pointers can be generated by the ECC; however, to extend the error correction beyond the usage of the ECC generated pointers, external error pointers are required.
The Reed-Solomon codes have been used with disk recording media in the form of so-called inner-outer codes. An outer code has sufficient redundancy for providing relatively powerful error detection and correction. The inner code may have a lesser redundancy and capability than the outer code. The inner code may be used as a source of error pointers to be used by the outer code. Both the inner and outer codes can be Reed-Solomon based codes.